W49N中的高能外流和减速膨胀
Extremely Energetic Outflow and Decelerated Expansion in W49N
摘要：
W 49 N是银河系中的一个小型星暴，因此是研究大质量恒星形成的理想实验室。由于其大的距离（11.1 $_{-0.7}^{+0.9}$ kpc），在W 49 N中的致密分子团内部和之间的运动学远未被很好地理解。SMA观测将连续发射分解为两个团块。SO $_{2}$（28 $_{4,24}$ -28 $_{3,25}$）的分子线观测表明，两团簇的速度差为$\sim$ 7 km~s $^{-1}$ .东丛与两个射电源“G1”和“G2”非常接近，而西丛与射电源“B”重合。HCN（3-2）线揭示了一种极高能量的外流，这是银河系中能量最高的分子外流之一。这是第一次在W 49 N中探测到高速分子外流。外流射流可能是进动的，这可以解释水脉泽斑的分布、速度和旋转。在HCO $^{+}$（3-2）谱图中识别出三个吸收系统。吸收特征相对于SO $_{2}$（28 $_{4,24}$ -28 $_{3,25}$）线的发射发生蓝移，表明冷层在暖气体前面膨胀。进一步的分析表明，膨胀是从几何膨胀中心减速。
英文摘要：
W49N is a mini-starburst in the Milky Way and thus an ideal laboratory for high-mass star formation studies. Due to its large distance (11.1$_{-0.7}^{+0.9}$ kpc), the kinematics inside and between the dense molecular clumps in W49N are far from well understood. The SMA observations resolved the continuum emission into two clumps. The molecular line observation of SO$_{2}$ (28$_{4,24}$-28$_{3,25}$) suggests that the two clumps have a velocity difference of $\sim$7 km~s$^{-1}$. The eastern clump is very close to two radio sources "G1" and "G2", and the western clump coincides with a radio source "B". The HCN (3-2) line reveals an extremely energetic outflow, which is among the most energetic molecular outflows in the Milky Way. This is the first report of high-velocity molecular outflow detection in W49N. The outflow jet might be in precession, which could account for the distribution, velocity and rotation of water maser spots. Three absorption systems are identified in HCO$^{+}$ (3-2) spectra. The absorption features are blueshifted with respect to the emission of SO$_{2}$ (28$_{4,24}$-28$_{3,25}$) lines, indicating that a cold layer is expanding in front of the warm gas. Further analysis indicates that the expansion is decelerated from the geometric expansion centers.
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